Dual-band capability in an infrared (IR) detector may have various sensing applications and may be constructed using a dual-band detector operated with a dual-polarity read-out integrated circuit (ROIC), or by using a single polarity ROIC and by implementing barriers and the selective depletion of the absorber. For example, such a system may require the selective depletion of a graded absorber to obtain a given voltage dependent spectral response. However, the application of a large reverse bias employed to deplete the absorber may result in increased generation-recombination (G-R) dark current which may diminish the performance of the device. Related art simultaneous mode detectors may operate in a mode in which they detect more than one band, but they may require special ROICs, and the three terminal architecture of the device may not be conducive to scaling to small pitch (small size).
Detectors with high quantum efficiency enhance the sensitivity of the detector. In an infrared (IR) detector, the quantum efficiency may be increased to some extent by increasing the thickness of the absorber layer. This approach however, may achieve only small increases in quantum efficiency for material systems that are limited by the minority carrier diffusion length. In some cases, increasing the thickness of the absorber can result in a decrease in the quantum efficiency (QE), for example if the minority carriers generated away from the junction cannot diffuse across the entire thickness of the absorber to the p-n junction or the collection area.
Thus, there is a need for a dual-band IR detector that provides high quantum efficiency in a material system limited by the minority carrier diffusion length.